Rotary machines include, without limitation, turbines for steam turbines and compressors and turbines for gas turbines. A steam turbine has a steam path which typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas-path leakage in the turbine or compressor area of a gas turbine, between the rotor of the turbine or compressor and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
Hybrid labyrinth-brush seals have been proposed for use between a rotor and a surrounding casing in gas and steam turbines. The annular hybrid seal includes circumferentially-arrayed hybrid seal segments positioned in a circumferential groove in the casing. Each hybrid seal segment has the shape of generally an annular segment of a circular ring. One or more of the rows of radially-inwardly-projecting and circumferentially-extending stainless-steel labyrinth-seal teeth are replaced with brush-seal bristles. The teeth of a labyrinth seal segment of a labyrinth seal have radially-cut circumferential ends, and the bristles of a brush seal segment of a brush seal are canted at typically a forty-five degree angle with respect to a radius line. For a hybrid labyrinth-brush seal segment, making the circumferential ends of the tooth portion of a seal segment have a forty-five degree cant angle to match the bristles will create teeth with very sharp circumferential ends which creates a safety hazard to persons installing or replacing the seal segments. For a hybrid labyrinth-brush seal segment, trimming the circumferential ends of the angled bristle portion of a seal segment to prevent the bristles from circumferentially extending beyond the radially-cut circumferential ends of the tooth portion of a seal segment will leave a short circumferential region of the seal segment without any bristles contacting the rotor resulting in increased seal leakage.